The invention concerns a method for automatically controlling the pressure of a common rail system on an A side and a common rail system on a B side of a V-type internal combustion engine.
V-type internal combustion engines have a rail on the A side and on the B side for temporary storage of the fuel. The injectors, which are connected to the rails, inject the fuel into the combustion chambers. In a first design of the common rail system, a high-pressure pump pumps the fuel into both rails at the same time, which is accompanied by an increase in pressure. Therefore, the same rail pressure prevails in both rails. A second design of the common rail system differs from the first in that a first high-pressure pump pumps the fuel into a first rail, and a second high-pressure pump pumps the fuel into a second rail. Both designs are described, for example, by DE 43 35 171 C1.
Since the quality of the combustion is critically dependent on the pressure level in the rails the pressure level is automatically controlled. Typically, a closed-loop pressure control system comprises a pressure controller, the suction throttle with high-pressure pump, the rail as the controlled system, and a filter in the feedback path. In this closed-loop pressure control system, the pressure level in the rail is the controlled variable. The measured raw values of the rail pressure are converted by the filter to an actual rail pressure, which is compared with a set rail pressure. The resulting control deviation is then converted by the pressure controller to a control signal for the suction throttle. The control signal corresponds to a volume flow in units of liters/minute, which is implemented electrically as a PWM (pulse-width-modulated) signal. A corresponding closed-loop pressure control system is known from DE 10 2006 049 266 B3.
An internal combustion engine provided as a generator drive is operated to realize a constant 50 Hz mains frequency in a closed-loop speed control system. The raw values of the controlled variable, i.e., the speed of revolution, are detected on the crankshaft, filtered, and compared as the actual speed with a reference input, the set speed. The resulting control deviation is then converted by a speed controller to the correcting variable, a set injection quantity.
A load reduction is a process that is difficult to control in an internal combustion engine with closed-loop pressure control and closed-loop speed control, first, due to its dynamics and, second, due to the different step response times of the two closed-loop control systems. Previously known measures for improving the response time in a load reduction, are regulation of injection start (DE 199 37 139 C1), switching to a faster speed filter (DE 10 253 739 B3) or pressure filter (DE 10 2004 023 365 A1), or temporarily increasing the PWM signal. In addition, DE 101 12 702 A1 discloses that in the case of large changes in dynamics, the response time of the closed-loop pressure control system can be improved by an input control variable. The high-pressure pump is controlled by the input control variable. The input control variable is computed from the set fuel quantity, the speed of the high-pressure pump, and the rail pressure.
A common feature of the methods described above is their use with a closed-loop pressure control system in a common rail system of the first design.